linux-kernel - Re: [PATCH 2/2] uevent: handle duplicate uevent

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Message-Id: <1220016439.24737.18.camel@lgn.site>
Date:	Fri, 29 Aug 2008 15:27:19 +0200
From:	Kay Sievers <kay.sievers@...y.org>
To:	Tejun Heo <tj@...nel.org>
Cc:	Greg KH <greg@...ah.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	David Zeuthen <david@...ar.dk>
Subject: Re: [PATCH 2/2] uevent: handle duplicate uevent_var keys properly

On Fri, 2008-08-29 at 10:02 +0200, Tejun Heo wrote:
> Kay Sievers wrote:
> > Not sure if I understand that correctly. Remember, that there is a
> > symlink "subsystem" at each device, and udev, HAL, DeviceKit reads it.
> > If the uevent environment key "SUBSYSTEM" does not match the symlink
> > target, things will break horribly. So no device can be a member of
> > class "cuse" but carry a SUBSYSTEM value of a different class.
> >
> > If that is how it works, I guess that must be solved differently, by
> > hooking into the subsystem code and create "virtual devices" at the
> > original class they fake, instead of their own "cuse" class. Possibly
> > by making cuse a "bus", and use the cuse device as a parent for the
> > "real" class device.
> 
> For OSS emulation, it didn't really matter.  For cases where it matters,
> I think easier path to take would be let the userland emulation set up a
> directory containing pseudo files and just override DEVPATH to it.
> Would that work?

No, I don't think so, it's a too bad hack. the SUBSYSTEM key, the entry
in the class/bus directory, and the target of the symlink in the device
directory _must_ match. Everything else asks for serious trouble, by the
inconsistency it creates.

Thanks,
Kay

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